Intrinsic Silicon Substrate Research Articles

Wide-bandgap semiconductor SiC-based memristors fabricated entirely by electron beam evaporation for artificial synapses

The combination of high-performance materials and simplified multilayer fabrication processes can promote the rapid and high-quality development of memristors. In this work, we proposed wide-bandgap semiconductor silicon carbide (SiC)-based memristors fabricated entirely by electron beam evaporation technology. The Cu/SiC/Pt structure was fabricated on a 2-inch intrinsic silicon substrate, which can achieve a transition from volatility to non-volatility. Devices had a low and symmetric switching voltage of ±0.5 V, an endurance of >200 cycles, a retention of >103 s, an ON/OFF ratio of ∼103, and can achieve at least 6 different stable resistance states. The combined effects of traps and Cu conductive filaments caused the current to change abruptly during switching, while also possessing excellent synaptic plasticity and pulse programming ability. Our work demonstrated that wide-bandgap semiconductor SiC is a promising candidate for advanced memristors.

Molecular beam epitaxy growth of topological insulator Bi4Br4 on silicon for the infrared applications

Bi4Br4 is a material rich in intriguing topological properties. Monolayer Bi4Br4 film exhibits helical edge states characteristic of a quantum spin Hall insulator, while bulk Bi4Br4 represents a higher-order topological insulator with hinge states. However, direct exfoliation from single crystal can only obtain thin nanowires due to the weak van der Waals forces between Bi4Br4 chains, which limits its optical analysis and application, while the growth of Bi4Br4 thin films is also full of challenges due to the extremely narrow growth temperature range and the accurate control of the BiBr3 flux. Here, we reported the controlled growth of α-Bi4Br4 thin films on intrinsic silicon substrates using molecular beam epitaxy. The growth temperature, BiBr3 flux, and the flux ratio of Bi and BiBr3 were accurately controlled. Then, the morphology, composition, and bonding of the prepared films were investigated using atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The growth of large, uniform thin films provides an ideal material platform for studying the physical properties of Bi4Br4. Additionally, we utilized Fourier-transform infrared spectroscopy to explore the film’s infrared characteristics, revealing strong absorption in the low frequency range due to the high proportion of one-dimensional topological edge states and laying the groundwork for further exploration of its potential applications in the optoelectronic field.

Prospects of silicide contacts for silicon quantum electronic devices

Metal contacts in semiconductor quantum electronic devices can offer advantages over doped contacts, primarily due to their reduced fabrication complexity and lower temperature requirements during processing. Some metals can also facilitate ambipolar device operation or form superconducting contacts. Furthermore, a sharp metal–semiconductor interface allows for contact placement in close proximity to the active device area avoiding damage caused by dopant implantation. However, in the case of gate-defined quantum dots in intrinsic silicon, the formation of a Schottky barrier at the silicon–metal interface can lead to large, nonlinear contact resistances at cryogenic temperatures. We investigate this issue by examining hole transport through metal oxide-semiconductor transistors with platinum silicide contacts on intrinsic silicon substrates. We extract the contact and channel resistances as a function of temperature and improve the cryogenic conductance of the device by more than an order of magnitude by implementing meander-shaped contacts. In addition, we observe signatures of enhanced transport through localized defect states, which we attribute to platinum clusters in the depletion region of the Schottky contacts that form during the silicidation process. These results showcase the prospects of silicide contacts in the context of cryogenic quantum devices and address associated challenges.

Preparation and characterization of Cu2ZnxFe1−xSnS4 thin ‎films deposited on intrinsic silicon substrates

The present paper reports the study of the effect of zinc content in Cu2Zn1−xFexSnS4 thin films. To achieve this purpose, CZTS, CZ0.5F0.5TS and CZTS thin films were grown at room temperature via thermal evaporation on unheated silicon substrates, which was followed by sulfidation at 400 °C. Analysis by x-ray diffraction indicates the polycrystalline nature of the CZFTS films with a preferential orientation along the (112) plane with structural transition from stannite (x = 0) to kesterite (x = 1) as the zinc content increases. The elemental composition of all thin films was analyzed by the EDAX technique. Morphological patterns were also explored in order to better understand the evolution of grain size and thickness as a function of zinc content. Hall effect measurements showed that the highest conductivity was obtained for CZTS. Impedance spectroscopy (IS) was performed between 5 Hz and 13 MHz. The complex impedance plots of the different samples revealed a single semicircle, suggesting that the response comes from a single capacitive element consistent with the grains. This measurement (IS) confirmed the enhancement of the conduction mechanism with increasing x-fraction. Experimental data suggested that AC conductivity in thin films C(Z, F)TS is proportional to ωs (s < 1). This is consistent with the correlated barrier hopping (CBH) model.

Microwave-to-optical conversion with a gallium phosphide photonic crystal cavity

Electrically actuated optomechanical resonators provide a route to quantum-coherent, bidirectional conversion of microwave and optical photons. Such devices could enable optical interconnection of quantum computers based on qubits operating at microwave frequencies. Here we present a platform for microwave-to-optical conversion comprising a photonic crystal cavity made of single-crystal, piezoelectric gallium phosphide integrated on pre-fabricated niobium circuits on an intrinsic silicon substrate. The devices exploit spatially extended, sideband-resolved mechanical breathing modes at ~3.2 GHz, with vacuum optomechanical coupling rates of up to g0/2π ≈ 300 kHz. The mechanical modes are driven by integrated microwave electrodes via the inverse piezoelectric effect. We estimate that the system could achieve an electromechanical coupling rate to a superconducting transmon qubit of ~200 kHz. Our work represents a decisive step towards integration of piezoelectro-optomechanical interfaces with superconducting quantum processors.

Investigation and Design of Dual Gate Dielectrically Modulated Junction less TFET for Biomolecule Recognition

This paperwork includes a tunnelling transistor with dual gate and employing the use of dielectric modulation (DG-DM-JL-TFET) based structure. In order to recognize the biomolecule like protein, biotin, uricase etc a nano cavity is presented above the tunnelling. Charge plasma technique is used to form the drain and source regions into the substrate. High work function creates a hole in source and similarly a lower work function will create an electron in drain. The “N” region is etched into the substrate using hafnium electrode with a work function of 3.9 eV. Si02 of 0.5nm thickness is inserted between electrode of source. The “P+” region is etched on intrinsic silicon substrate using Platinum electrode having a work function of 5.93 eV. The device structure proposed in this paper shows results for sensitivity for charged and neutral biological molecules. The sensitivity of the biological molecules having higher dielectric constant is greater than those biological molecules possessing lower dielectric constant.

Metalorganic Chemical Vapor Phase Epitaxy Growth of Buffer Layers on 3C‐SiC/Si(111) Templates for AlGaN/GaN High Electron Mobility Transistors with Low RF Losses

Herein, the interest of cubic silicon carbide as a template for the growth of AlGaN/GaN high electron mobility transistor (HEMT) heterostructures on silicon substrates for high‐frequency operation is shown. On the one hand, 0.6–0.8 μm‐thick 3C‐SiC grown by chemical vapor deposition on intrinsic silicon substrate having initial resistivity superior to 5 kΩ cm enables the metalorganic vapor phase epitaxy of GaN buffer layers with propagation losses below 0.4 dB mm−1 at 40 GHz and 0.5 dB mm−1 at 67 GHz. On the other hand, an HEMT heterostructure is grown on 1.5 μm‐thick 3C‐SiC on 4° off‐axis silicon substrate having an initial resistivity superior to 200 Ω cm that allows to keep a sufficiently resistive epilayer stack limiting the loss up to 0.78 dB mm−1 at 40 GHz. Device process developed on a piece of the 100 mm diameter wafer leads to the demonstration of DC transistor operation with low leakage currents. Compared with direct growth on silicon, these templates enable reduced radio frequency (RF) propagation losses that are very interesting for high‐frequency transistors and circuits operation.

Photoinduced Hall Effect for Low-Temperature Magnetic Sensing

Some low-temperature magnetic sensors are based on the Hall effect in thin metallic films. However, their sensitivity is more than one order of magnitude smaller than that of silicon-based Hall sensors operating at room temperature. Furthermore, in order to avoid significant Joule heating, only very small bias currents can be injected at low temperatures. Here, we show that a sensor based on a photoinduced Hall effect, in which charge is photogenerated in a semiconductor and injected into an adjacent metallic layer, can be used as a bias-free, cryogenic sensor. The system consists of a platinum thin film deposited on intrinsic-silicon substrate. The film forms a Schottky interface with the semiconductor. At room temperature, carriers photogenerated in the semiconductor are injected into the metal, because of rounding-off of the Schottky barrier, and are deflected by a magnetic field applied in the film plane. At cryogenic temperatures, and well below the freeze-out temperature for silicon, the photogenerated electrons can tunnel through the barrier, and the sensor recovers the same sensitivity as that obtained at room temperature.

Infrared micropolarizer array fabricated using a reversal nanoimprint.

Using a reversal nanoimprint and metal evaporation process, we fabricated a micropolarizer array for the 2.5-7μm wavelength region. The micropolarizer array has a unique unit, which is composed of 2×3 arrays on an intrinsic silicon substrate. Each array consists of a 200nm period bilayer Al grating in a 1.3 mm×1.3 mm aperture. The transmittance of transverse magnetic polarization of each array is greater than 65% in the 2.5-7μm wavelength range, and the extinction ratio is over 35dB in the 3-4μm and 6-7μm wavelength range. This fabricated micropolarizer array has lower costs and better compatibility with microfabrication processes.

Deep level transient spectroscopic investigation of phosphorus-doped silicon by self-assembled molecular monolayers

It is known that self-assembled molecular monolayer doping technique has the advantages of forming ultra-shallow junctions and introducing minimal defects in semiconductors. In this paper, we report however the formation of carbon-related defects in the molecular monolayer-doped silicon as detected by deep-level transient spectroscopy and low-temperature Hall measurements. The molecular monolayer doping process is performed by modifying silicon substrate with phosphorus-containing molecules and annealing at high temperature. The subsequent rapid thermal annealing drives phosphorus dopants along with carbon contaminants into the silicon substrate, resulting in a dramatic decrease of sheet resistance for the intrinsic silicon substrate. Low-temperature Hall measurements and secondary ion mass spectrometry indicate that phosphorus is the only electrically active dopant after the molecular monolayer doping. However, during this process, at least 20% of the phosphorus dopants are electrically deactivated. The deep-level transient spectroscopy shows that carbon-related defects are responsible for such deactivation.

Surface-Enhanced Infrared Absorption of Self-Aligned Nanogap Structures

Plasmonic nanostructures are often used in surface-enhanced infrared absorption (SEIRA) spectroscopy to probe surface assembled molecules or the dielectric environment surrounding the metallic nanostructures. Here we fabricate metallic nanogap structures using self-aligned techniques on an intrinsic silicon substrate and correlate resulting SEIRA spectra with the choice of metal nanostructure geometry. A motivation is to compare the enhancement from hybridization of bright plasmon modes with the effect of hybridization between bright and dark plasmon modes. These structures provide a gap size below 10 nm and support strong field enhancements. The structures demonstrate their sensitivity through the enhanced absorption signature of the Si–O stretch in the native silicon oxide layer of nanometer thickness beneath the metal. Simulations reveal this thin layer plays a critical role in determining the plasmon modes of the nanostructures. Numerical simulations of the optical properties are consistent with the observations that stronger Si–O stretch signals are detected on self-aligned nanogap structures than nanorod arrays, highlighting the enhanced electromagnetic fields in the underlying native oxide.

Cr-Doped TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Thin Films Prepared by Means of a Magnetron Co-Sputtering Process: Photocatalytic Application

This paper deals with the effect of Cr content on photocatalytic activity of TiO2 thin films deposited on quartz and intrinsic silicon substrates by using the RF magnetron co-sputtering process. Some physical investigations on such sputtered films were made by means of X-ray Diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy as well as UV-Vis-IR absorption techniques. The heat treatment under oxygen atmosphere at 550°C reveals that the crystalline structure of TiO2: Cr depends on Cr content. Anatase-to-rutile phase transformation occurs at a Cr content of about 7%. On the other hand, the band gap energy value of annealed TiO2: Cr films varies in terms of Cr doping and a transition around 7% of Cr is accrued. The photocatalytic activity of undoped and doped TiO2 films was evaluated by photo-degrading of the amido black under UV light irradiation. Modification of the chemical structure of titanium dioxide by Cr doping allows moving the photocatalytic activity of titanium dioxide towards visible light. The results indicate that films doped with 2% Cr exhibit the highest UV and visible light photocatalytic activity.

Hole Doping Through Indium Intercalation into Copper Phthalocyanine

A blend of molecular acceptor and molecular donor made of Copper Phthalocyanine (CuPc) and Indium in various ratios were evaporated in high vacuum on to intrinsic silicon substrates by using vacuum thermal co-evaporation technique. Electronic properties of In-doped CuPc thin films have been examined by X-ray photoelectron spectroscopy (XPS). The results obtained by XPS suggests that In-doped CuPc is a hole transport material.

A comparative study on comb electrodes devices made of MWPECVD diamond films grown on p-doped and intrinsic silicon substrate

Diamond is considered as a very promising material for the development of devices for radiation detection. Unlike other conventional photoconductive detectors diamond-based devices should provide high discrimination between UV and visible radiation. In this work we present the electro-optical properties of devices based on randomly oriented diamond films, synthesized in a microwave plasma enhanced chemical vapor deposition reactor. A comparative study on devices with coplanar interdigitated Cr/Au electrodes (with different interelectrode pitches) made of films grown simultaneously on intrinsic and p-doped silicon (100) substrates has been performed. The chemical–structural, morphological, electrical and optical properties of ROD films have been studied. In particular, the optical response has been measured in air using a Xe flash lamp coupled with an optical quartz fiber and a properly tailored front-end electronics based on a charge sensitive amplifier. Experimental results gave indications on how the device performances are dependent on the two types of employed substrates.

Deeply-etched singlemode GeSi rib waveguides for silicon-based optoelectronic integration

The fabrication and characterisation of deeply-etched single-mode GeSi rib waveguides, grown on an intrinsic silicon substrate, for monolithic optoelectronic integration are reported. The waveguides exhibit strong singlemode guiding and good confinement with a propagation loss of ∼2.5±1dB/cm at 1.3μm.

Modulation of space-charge-limited current flow in insulated-gate field-effect tetrodes

The electrical characteristics of n-channel depletion-type and p-channel enhancement-type space-charge-limited tetrodes are presented. The devices are derived from the MOSFET structure and are fabricated on nearly intrinsic silicon substrates with very small channel lengths. In both structures, the current flowing between drain and source can be modulated by either of two high-impedance control terminals. The dominant conduction mechanism is space-charge-limited current flow, and the observed current-voltage characteristics of each device follow the Mott and Gurney relationship at high current levels.